The purpose of this four-year study, School Worksite Weight Gain Prevention Intervention Study, is to determine the effectiveness of an ecological worksite intervention compared to a self-directed, print-materials only control group at reducing weight gain among public high school employees in Massachusetts. The intervention, called Step Ahead, is a comprehensive intervention targeting the three levels suggested by ecological frameworks for health behavior change: (1) the organizational (school) level, (2) the interpersonal level, and (3) the individual level. A social marketing campaign will integrate all program activities using common logos, themes and messages. Evaluation of the proposed intervention will be by a randomized controlled trial (RCT) in which the unit of randomization and intervention is the school worksite and the unit of evaluation and inference is the employee. Eighteen schools will be stratified into three strata: large urban, small urban or rural schools. Within each stratum, schools will be randomized to either the ecological intervention or print materials only control condition. A total of 540 teachers and staff from 18 schools will be enrolled and retained, 360 from intervention and 360 from control sites. Assessments will be completed at five time points: baseline, 6 months, 12 months, 18 months and 24 months. The primary aim of this study is to determine the effectiveness of the intervention in preventing employee weight gain, as measured by change in BMI and waist circumference, over the 24- month intervention period. Secondary aims include determining the effects of the intervention on physical activity, caloric intake, saturated fat intake and consumption of fruits and vegetables among employees, as well determining the effects on absenteeism and presenteeism. Tertiary aims are to determine the effects of the intervention on mediating and moderating factors, including perceived organizational commitment to employee health, perceived co-worker normative influences for healthy eating and physical activity, social support for healthy behaviors, self-efficacy and self- control. The proposed study builds off of the study team's previous studies and experiences in designing, implementing and evaluating ecological worksite interventions and in conducting large-scale randomized controlled trials in the high school setting. There are three phases to the investigation: Phase I: Recruitment of schools and intervention and instrumentation refinement; Phase II: Intervention implementation and evaluation; Phase III: Analysis and dissemination. PUBLIC HEALTH RELEVANCE: The proposed site-level randomized trial will test the effectiveness of a worksite intervention based on an ecological framework at preventing weight gain among high school employees in Massachusetts. If effective, the intervention is designed to be generalizable to high school settings across the country and has the potential to reduce the morbidity, mortality and economic costs of overweight and obesity in this important population.